Biologique Recherche purifying & stabilizing masks are the last products that are applied before the Treatment Stage. They contain high concentrations of active ingredients to balance and purify the epidermis and preserve all the benefits of previous treatments. Biologique Recherche purifying & stabilizing masks contain Essential Fatty Acids to replenish the skins proteo-lipidic film after exfoliation and prepare the skin for the products that are applied during the Treatment Stage. Unlike other brands, at Biologique Recherche the masks are applied in the middle of the skin care program and not at the end. This is done deliberately to avoid removing the active ingredients used in the Treatment Stage along with the mask.